Evaporator and centrifugal chiller provided with the same

ABSTRACT

The present invention maintains a compact evaporator size in a centrifugal chiller utilizing a low pressure refrigerant used at a maximum pressure of less than 0.2 MPaG while avoiding efficiency losses and equipment damage that result from carryover of liquid state refrigerant to the turbo compressor side. This evaporator is equipped with a pressure vessel into which a condensed refrigerant is introduced, a refrigerant inlet which is provided to the bottom portion of the pressure vessel, a refrigerant outlet which is provided to the top portion of the pressure vessel, a heat transfer pipe group which passes through the interior of the pressure vessel, circulates liquid to be chilled through the interior thereof, and exchanges heat between the liquid to be chilled and the refrigerant, and a demister which is disposed between the refrigerant outlet and the heat transfer pipe group in the interior of the pressure vessel and carries out vapor-liquid separation of the refrigerant, a dividing section (for example, a plurality of notches) being provided between the periphery of the demister and the inner peripheral surface of the pressure vessel. The dividing section is provided to a side of the demister along the lengthwise direction.

TECHNICAL FIELD

The present invention relates to an evaporator gasifying a low pressure refrigerant, and a centrifugal chiller provided with the same.

BACKGROUND ART

For example, as is well known, a centrifugal chiller used as a heat source for district cooling and heating is configured to include a turbo compressor that compresses a refrigerant, a condenser that condenses the compressed refrigerant, an expansion valve that expands the condensed refrigerant, and an evaporator that evaporates the expanded refrigerant.

PTL 1 discloses a so-called pool-boiling shell-and-tube-type evaporator which is generally used as an evaporator of a centrifugal chiller. Such an evaporator includes a cylindrically shell-shaped pressure container extending in a horizontal direction, in which a group of heat transfer pipes serving as passages for a cooling target liquid such as water is arranged so as to penetrate the pressure container in a longitudinal axis direction. In addition, inside the pressure container, a refrigerant distribution plate having a number of refrigerant circulation holes bored therein is provided below the group of heat transfer pipes, and a demister (also referred to as an eliminator or a mist separator) is provided above the group of heat transfer pipes.

After a liquid-phase refrigerant compressed in a turbo compressor and condensed in the condenser is reduced in pressure by an expansion valve, the liquid-phase refrigerant flows into the pressure container through a refrigerant inlet provided in a lower portion of the pressure container and passes through a number of refrigerant circulation holes in the refrigerant distribution plate. Then, the liquid-phase refrigerant is diffused throughout the entire region inside the pressure container and is stored up to a liquid level at which the group of heat transfer pipes is submerged, thereby being subjected to heat exchange with the group of heat transfer pipes. Consequently, the cooling target liquid flowing inside the group of heat transfer pipes is cooled, and this cooled cooling target liquid is utilized as a cooling/heating medium for air conditioning or an industrial cooling liquid.

A liquid-phase refrigerant which has been subjected to heat exchange with the group of heat transfer pipes is gasified (boils) due to the temperature difference. A liquid-phase part is eliminated when passing through the demister, and only a gas-phase refrigerant comes out through a refrigerant outlet provided in an upper portion of the pressure container and is suctioned to the turbo compressor, thereby being compressed again.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No. 61-280359

SUMMARY OF INVENTION Technical Problem

Low pressure refrigerants such as R1233zd used at a maximum pressure of less than 0.2 MPaG are expected as next generation refrigerants because they can improve efficiency of a centrifugal chiller and have a low global warming potential. Since such low pressure refrigerants are characterized in material by the gas specific volume which increases approximately five times the gas specific volume of a high pressure refrigerant such as R134a, when a low pressure refrigerant is subjected to heat exchange with a group of heat transfer pipes and boils inside an evaporator, boiling froth increases, thereby being in an intense boiling state. Furthermore, since the volumetric flow rate of a gasified refrigerant inside the evaporator is extremely greater than that of a high pressure refrigerant, the flow velocity of the gasified refrigerant inside the evaporator increases.

Therefore, inside a pressure container, gas-liquid separation is not completely performed by a demister, thereby being likely to cause a phenomenon that is so called carry-over (gas-liquid entrainment) in which a liquid-phase refrigerant (droplet) that has not yet gasified hitches a fast flow of a gasified refrigerant flowing toward a refrigerant outlet and is released through the refrigerant outlet. When such droplets of a refrigerant which have not been completely evaporated are suctioned into a turbo compressor, there is concern that the compression ratio of the turbo compressor may deteriorate and the efficiency may be degraded, so that a blade or the like of the turbo compressor may be damaged.

Therefore, the diameter of the pressure container is increased such that carry-over is unlikely to occur, and the flow velocity of a gasified refrigerant inside the pressure container is reduced by increasing the pipe pitch of the group of heat transfer pipes. In addition, the height difference between the group of heat transfer pipes and the refrigerant outlet is increased so as to enhance the effect in which droplets of a refrigerant are separated from a gasified refrigerant due to their dead weight. Moreover, countermeasures of capturing droplets of a refrigerant are adopted by disposing the demister in the vicinity of the refrigerant outlet.

However, consequently, the dimensions and the shape of each portion of the evaporator including the pressure container increase, so that compactness of the centrifugal chiller is impaired.

The present invention has been made in consideration of such circumstances, and an object thereof is to provide an evaporator, in a centrifugal chiller using a low pressure refrigerant used particularly at a maximum pressure of less than 0.2 MPaG, in which while compactness of the evaporator is retained, deterioration in efficiency or damage to the device caused by a liquid-phase refrigerant carried over to a turbo compressor side can be avoided, and a centrifugal chiller provided with the same.

Solution to Problem

In order to solve the problems, the present invention employs the following means.

According to a first aspect of the present invention, there is provided an evaporator including a pressure container into which a condensed refrigerant is introduced; a refrigerant inlet which is provided in a lower portion of the pressure container; a refrigerant outlet which is provided in an upper portion of the pressure container; a group of heat transfer pipes which passes through an inside of the pressure container and circulates a cooling target liquid inside the group of heat transfer pipes to cause the cooling target liquid to be subjected to heat exchange with the refrigerant; and a demister which is installed between the refrigerant outlet and the group of heat transfer pipes inside the pressure container and performs gas-liquid separation of the refrigerant. A separation portion is provided between a circumferential portion of the demister and an inner circumferential surface of the pressure container.

As described above, since the separation portion is provided between the circumferential portion of the demister performing gas-liquid separation of a refrigerant and the inner circumferential surface of the pressure container, droplets of a refrigerant which have passed through the demister upward from below can promptly return to a lower part of the demister via the separation portion. Therefore, the quantity of refrigerant droplets staying in an upper part of the demister can be reduced and the refrigerant droplets can be prevented from hitching a flow of a gasified refrigerant and being carried over to a turbo compressor side through the refrigerant outlet.

Then, since the quantity of refrigerant droplets on the demister can be reduced as described above, the necessity of reducing the flow velocity of a gasified refrigerant inside the pressure container by increasing the diameter of the pressure container or increasing the pipe pitch of the group of heat transfer pipes decreases. Therefore, in a case of using a low pressure refrigerant used particularly at a maximum pressure of less than 0.2 MPaG, while compactness of the evaporator is retained, deterioration in efficiency or damage to the device caused by a liquid-phase low pressure refrigerant carried over to the turbo compressor side can be suppressed.

In the configuration described, the pressure container may be configured to have a cylindrical shell shape extending in a horizontal direction. The separation portion may be configured to be provided on a side of the demister along an axis direction of the pressure container.

In a case where the inside of the pressure container having a cylindrical shell shape is seen in the axis direction, a gasified refrigerant which has passed through the demister upward from below forms an upward air current toward the refrigerant outlet provided at the center of the upper portion of the pressure container. At the same time, a downward air current drawing a loop downward is formed on both sides of the upward air current. This downward air current is headed for the separation portion of the demister along an inner surface of a cylinder-shaped pressure container. Therefore, refrigerant droplets which have passed through the demister can be induced into the separation portion due to the downward air current and can return to a lower part of the demister. Accordingly, refrigerant droplets which have passed through the demister can more effectively return to the lower portion of the demister and can be prevented from being carried over to the turbo compressor side.

In the configuration described, the pressure container may be configured to have a cylindrical shell shape extending in a horizontal direction. The group of heat transfer pipes may be configured to be installed to pass through the inside of the pressure container in a longitudinal axis direction. The separation portion may be configured to be provided to be biased to an upstream portion side of the group of heat transfer pipes.

On the upstream portion side of the group of heat transfer pipes inside the pressure container having a cylindrical shell shape, a liquid refrigerant intensely boils due to a significant difference between relative temperatures of the cooling target liquid flowing inside thereof and the liquid refrigerant. However, the boiling degree of the liquid refrigerant decreases toward a downstream side of the group of heat transfer pipes. Therefore, the separation portion is provided at a position where the liquid refrigerant boils intensely and droplets of a liquid refrigerant are likely to pass through the demister, so that refrigerant droplets which have passed through the demister can promptly return from the separation portion to a lower part of the demister and can be effectively prevented from being carried over to the turbo compressor side.

In the configuration described, the pressure container may be configured to have a cylindrical shell shape extending in a horizontal direction. The group of heat transfer pipes may be configured to include a group of outbound pipes extending from one end to the other end in the longitudinal axis direction inside the pressure container, and a group of inbound pipes communicating with the group of outbound pipes at the other end in the longitudinal axis direction inside the pressure container and returning from the other end to the one end in the longitudinal axis direction inside the pressure container. The group of outbound pipes may be configured to be disposed below and the group of inbound pipes may be configured to be disposed above inside the pressure container.

According to this configuration, the group of outbound pipes in which a difference between relative temperatures of the cooling target liquid flowing inside the heat transfer pipes and the liquid refrigerant is significant and the liquid refrigerant intensely boils is disposed in the lower portion of the pressure container. The group of inbound pipes in which the temperature difference between the cooling target liquid and the liquid refrigerant is small and the liquid refrigerant boils gently is disposed in the upper portion of the pressure container. Therefore, the liquid refrigerant intensely boils in a deep part of a liquid refrigerant pool inside the pressure container, so that refrigerant droplets are unlikely to scatter on a liquid surface of the liquid refrigerant.

In addition, due to a layout in which the group of outbound pipes and the group of inbound pipes vertically overlap each other, for example, compared to a case of a layout in which the group of outbound pipes and the group of inbound pipes laterally overlap each other, the amount of air bubbles of the liquid refrigerant which comes into contact with the group of outbound pipes and boils can be uniform throughout the pressure container in a width direction.

Accordingly, a flow of an upward air current of a gasified refrigerant in an upper part of the demister is laterally equalized, and a part having a high flow velocity is prevented from being locally generated, so that it is possible to prevent refrigerant droplets from being carried over to the turbo compressor side due to a flow of a gasified refrigerant at a high flow velocity.

In the configuration described, the demister may be configured to be disposed immediately above the group of heat transfer pipes.

In a case where the low pressure refrigerant is used, since the gas flow velocity is high, the distance to a position where droplets of a liquid refrigerant spouting upward are separated from a gasified refrigerant due to their dead weights becomes comparatively long. Therefore, when the demister is installed at a position higher than the position where the droplets are separated due to their dead weights, the distance from the liquid surface of the refrigerant to the demister becomes long, and the pressure container increases in shell diameter.

When the demister is disposed immediately above the group of heat transfer pipes as described above, the quantity of droplets spouting upward is reduced by the demister, so that the carry-over amount can be reduced. Moreover, when the demister is disposed immediately above the group of heat transfer pipes, evaporated mist of the low pressure refrigerant is promoted to be droplets having a large diameter in the space above the demister, and the distance to the position where the droplets are separated due to their dead weights is shortened, so that it is possible to prevent the low pressure refrigerant from being carried over.

According to a second aspect of the present invention, there is provided a centrifugal chiller including a turbo compressor which compresses a low pressure refrigerant used at a maximum pressure of less than 0.2 MPaG, a condenser which condenses the compressed low pressure refrigerant, and the evaporator according to any one of claims 1 to 5, which evaporates the expanded low pressure refrigerant. Accordingly, it is possible to exhibit each of the operations and the effects described above.

Advantageous Effects of Invention

As described above, according to the evaporator of the present invention and the centrifugal chiller provided with the same, in a centrifugal chiller using a low pressure refrigerant used particularly at a maximum pressure of less than 0.2 MPaG, in which while compactness of the evaporator is retained, deterioration in efficiency or damage to the device caused by a liquid-phase refrigerant carried over to a turbo compressor side can be avoided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general view of a centrifugal chiller according to an embodiment of the present invention.

FIG. 2 is a longitudinal-sectional view of the evaporator taken along line II-II in FIG. 1.

FIG. 3 is a longitudinal-sectional view of the evaporator taken along line III-III in FIG. 2.

FIG. 4 is a cross-sectional view of the evaporator taken along line IV-IV in FIG. 2.

FIG. 5 is a longitudinal-sectional view of the evaporator illustrating the embodiment of the present invention taken along line V-V in FIG. 4.

DESCRIPTION OF EMBODIMENT

Hereinafter, an embodiment of the present invention will be described with reference to the drawing.

FIG. 1 is a general view of a centrifugal chiller according to an embodiment of the present invention. A centrifugal chiller 1 is configured in a unit state including a turbo compressor 2 that compresses a refrigerant, a condenser 3, a high-pressure expansion valve 4, an economizer 5, a low-pressure expansion valve 6, an evaporator 7, a lubricant tank 8, a circuit box 9, an inverter unit 10, an operation panel 11, and the like. The lubricant tank 8 is a tank storing lubricant supplied to bearings, a speed increaser, and the like of the turbo compressor 2.

The condenser 3 and the evaporator 7 are formed into cylindrical shell shapes having high pressure resistance and are disposed so as to be parallel and adjacent to each other in a state where their axial lines extend in a substantially horizontal direction. The condenser 3 is disposed at a position relatively higher than the evaporator 7, and the circuit box 9 is installed below thereof. The economizer 5 and the lubricant tank 8 are installed while being interposed between the condenser 3 and the evaporator 7. The inverter unit 10 is installed in an upper portion of the condenser 3, and the operation panel 11 is disposed above the evaporator 7.

The turbo compressor 2 is a known centrifugal turbine-type compressor which is rotatively driven by an electric motor 13. The turbo compressor 2 is disposed above the evaporator 7 in a posture having its axial line extending in the substantially horizontal direction. The electric motor 13 is driven by the inverter unit 10. As described below, the turbo compressor 2 compresses a gas-phase refrigerant supplied through a refrigerant outlet 23 of the evaporator 7 via a suction pipe 14. A low pressure refrigerant such as R1233zd used at a maximum pressure of less than 0.2 MPaG, for example, is used as the refrigerant.

A discharge port of the turbo compressor 2 and the upper portion of the condenser 3 are connected to each other through a discharge pipe 15, and the bottom portion of the condenser 3 and the bottom portion of the economizer 5 are connected to each other through a refrigerant pipe 16. In addition, the bottom portion of the economizer 5 and the evaporator 7 are connected to each other through a refrigerant pipe 17, and an upper portion of the economizer 5 and a middle stage of the turbo compressor 2 are connected to each other through a refrigerant pipe 18. The high-pressure expansion valve 4 is provided in the refrigerant pipe 16, and the low-pressure expansion valve 6 is provided in the refrigerant pipe 17.

As illustrated in FIGS. 2 and 3, the evaporator 7 is configured to include a pressure container 21 having a cylindrical shell shape extending in the horizontal direction, a refrigerant inlet 22 provided in a lower portion of the pressure container 21, the refrigerant outlet 23 provided in an upper portion of the pressure container 21, a group of heat transfer pipes 25 passing through the inside of the pressure container 21 in a longitudinal axis direction, a refrigerant distribution plate 26, and a demister 27.

Each of the refrigerant inlet 22 and the refrigerant outlet 23 is formed into a cylindrical shell shape and is disposed at an intermediate portion in the longitudinal axis direction of the pressure container 21 of which the axial line extends in a substantially horizontal direction. The refrigerant inlet 22 is formed into a short pipe shape extending horizontally and tangentially from the bottom portion of the pressure container 21, and the refrigerant outlet 23 is formed into a short pipe shape extending vertically upward from the upper portion of the pressure container 21. As illustrated in FIG. 1, the refrigerant pipe 17 extending from the bottom portion of the economizer 5 is connected to the refrigerant inlet 22, and the suction pipe 14 of the turbo compressor 2 is connected to the refrigerant outlet 23.

An inlet chamber 31 is provided on a lower side at one end (for example, the left end in FIG. 2) and an outlet chamber 32 is provided above the inlet chamber 31, as independent rooms inside the pressure container 21. In addition, a U-turn chamber 33 is provided as an independent room at the other end (for example, the right end in FIG. 2) inside the pressure container 21. All these chambers 31, 32, and 33 are disposed lower than the demister 27. An inlet nozzle 34 is provided in the inlet chamber 31, and an outlet nozzle 35 is provided in the outlet chamber 32.

As illustrated in FIGS. 2, 3, and 5, the group of heat transfer pipes 25 includes a group of outbound pipes 25A extending from one end (the left end in FIG. 2) to the other end (the right end in FIG. 2) in the longitudinal axis direction inside the pressure container 21, and a group of inbound pipes 25B communicating with the group of outbound pipes 25A at the other end in the longitudinal axis direction inside the pressure container 21 and returning from the other end to the one end in the longitudinal axis direction inside the pressure container 21. Specifically, the group of outbound pipes 25A is arranged so as to link the inlet chamber 31 and a lower portion of the U-turn chamber 33 with each other, and the group of inbound pipes 25B is arranged so as to link the outlet chamber 32 and an upper portion of the U-turn chamber 33 with each other. That is, the group of outbound pipes 25A is disposed below inside the pressure container 21, and the group of inbound pipes 25B is disposed above inside the pressure container 21.

For example, as a cooling target liquid to be subjected to heat exchange with a refrigerant and to be cooled, water (tap water, purified water, distilled water, or the like) flows in through the inlet nozzle 34. The water which has flowed in through the inlet chamber 31 flows through the group of outbound pipes 25A and makes a U-turn in the U-turn chamber 33. Thereafter, the water flows through the group of inbound pipes 25B and flows out through the outlet nozzle 35 via the outlet chamber 32 as chilled water.

As illustrated in FIG. 3, the group of outbound pipes 25A and the group of inbound pipes 25B configuring the group of heat transfer pipes 25 have configurations in which a plurality (for example, four each) of heat transfer pipe bundles 25 a each having a number of heat transfer pipes bundled therein are arrayed in parallel in the horizontal direction. Gaps S1 extending in a vertical direction are formed among the heat transfer pipe bundles 25 a. In addition, a gap S2 extending in the horizontal direction is formed between the group of outbound pipes 25A and the group of inbound pipes 25B.

As illustrated in FIG. 2, each of the heat transfer pipes configuring the group of heat transfer pipes 25 (25A, 25B) is fixed inside the pressure container 21 while being supported by a plurality of heat transfer pipe support plates 37 inside the pressure container 21. The heat transfer pipe support plates 37 are formed into flat plate shapes having a plane direction intersecting the longitudinal axis direction of the pressure container 21. The plurality of heat transfer pipe support plates 37 are disposed at intervals in the longitudinal axis direction of the pressure container 21 and are fixed to an inner surface of the pressure container 21. A number of penetration holes are bored in the heat transfer pipe support plates 37, and the heat transfer pipes are tightly inserted through the penetration holes.

Meanwhile, as illustrated in FIGS. 2, 3, and 5, the refrigerant distribution plate 26 is installed between the refrigerant inlet 22 and the group of heat transfer pipes (group of outbound pipes 25A) inside the pressure container 21. The refrigerant distribution plate 26 is a tabular member in which a number of refrigerant circulation holes 26 a are bored.

As illustrated in FIGS. 2, 3, and 5, the demister 27 is disposed between the refrigerant outlet 23 and the group of heat transfer pipes 25 (group of inbound pipes 25B) inside the pressure container 21. For example, the demister 27 is a member which has excellent air-permeability and in which wires are interwoven in a meshed state. The demister 27 performs gas-liquid separation of a low pressure refrigerant. The demister 27 is not limited to the wire mesh, and other porous matters may be employed as long as the matter is air-permeable.

As illustrated in FIG. 4 as well, the demister 27 is attached such that a peripheral edge portion thereof is in contact with the inner circumference of the pressure container 21, and an internal space of the pressure container 21 is divided into two above and below fiducially from the demister 27. In addition, the installation height of the demister 27 is set immediately above the group of heat transfer pipes 25 (25B). Specifically, the interval between the group of heat transfer pipes 25 (25B) and the demister 27 is set to approximately twice the pipe disposition pitch. Meanwhile, a comparatively significant difference in height (for example, approximately 50% or more of the diameter of the pressure container 21) is provided between the demister 27 and the refrigerant outlet 23.

As illustrated in FIGS. 5, 2, and 4, a separation portion 27A is provided between a circumferential portion of the demister 27 and an inner circumferential surface of the pressure container 21. The separation portion 27A is constituted by forming a plurality of rectangular cut-outs 27 a at equal intervals on each of both sides 27L and 27R of the demister 27 along an axis direction of the pressure container 21.

In addition, the separation portion 27A (cut-outs 27 a) is provided to be biased to an upstream portion side of the group of heat transfer pipes 25. That is, as illustrated in FIG. 2, the group of outbound pipes 25A configuring the upstream portion of the group of heat transfer pipes 25 is provided to be biased to a side leading to the inlet chamber 31 which is an inflow portion of the cooling target liquid. For example, the length of the separation portion 27A is set to range from approximately one fourth to approximately half the length of the demister 27 in the longitudinal direction.

The shape, the interval, the vertical and lateral size, the length, and the like of the separation portion 27A (cut-outs 27 a) are not necessarily limited to those disclosed in FIG. 4. For example, the number thereof may be reduced by increasing the length dimensions of the cut-outs 27 a, and the cut-outs 27 a may be formed into slit shapes instead of cut-out shapes. In addition, the cut-outs may have other shapes without being limited to the rectangular shape. Moreover, as a modification example, holes may be bored in place of the cut-outs 27 a. In addition, the separation portion 27A is not necessarily provided on both the sides 27L and 27R of the demister 27 and can be conceived to be provided on only one side.

In the centrifugal chiller 1 including the evaporator 7 configured as described above, the turbo compressor 2 is rotatively driven by the electric motor 13, compresses a gas-phase low pressure refrigerant supplied from the evaporator 7 via the suction pipe 14, and feeds this compressed low pressure refrigerant to the condenser 3 through the discharge pipe 15.

Inside the condenser 3, when a high temperature low pressure refrigerant compressed in the turbo compressor 2 is subjected to heat exchange with cooling water, condensed heat is cooled, so that the low pressure refrigerant is condensed and liquefied. The low pressure refrigerant caused to be in a liquid phase by the condenser 3 expands after passing through the high-pressure expansion valve 4 provided in the refrigerant pipe 16 extending from the condenser 3. The low pressure refrigerant is transported to the economizer 5 in a gas-liquid mixed state and is temporarily stored therein.

Inside the economizer 5, the low pressure refrigerant which has expanded through the high-pressure expansion valve 4 in a gas-liquid mixed state is subjected to gas-liquid separation into a gas-phase part and a liquid-phase part. The liquid-phase part of the low pressure refrigerant separated herein is caused to further expand through the low-pressure expansion valve 6 provided in the refrigerant pipe 17 extending from the bottom portion of the economizer 5 and becomes a gas-liquid two-phase flow, thereby being transported to the evaporator 7. In addition, the gas-phase part of the low pressure refrigerant separated in the economizer 5 is transported to a middle stage portion of the turbo compressor 2 via the refrigerant pipe 18 extending from the upper portion of the economizer 5 and is compressed again.

As illustrated in FIGS. 2 to 4, in the evaporator 7, the low pressure refrigerant which has adiabatically expanded through the low-pressure expansion valve 6 in a low temperature gas-liquid two-phase flow state flows into the pressure container 21 through the refrigerant inlet 22, is dispersed in the longitudinal axis direction of the pressure container 21 below the refrigerant distribution plate 26, and then passes through the refrigerant circulation holes 26 a of the refrigerant distribution plate 26, thereby flowing upward. Then, a pool for the low pressure refrigerant is formed inside the pressure container 21. The liquid level in the low pressure refrigerant pool is automatically adjusted so as to be between the group of heat transfer pipes 25 (25B) and the demister 27.

The group of heat transfer pipes 25 (25A, 25B) is in a state of being immersed in the low pressure refrigerant pool inside the pressure container 21 and is subjected to heat exchange with the low pressure refrigerant. Accordingly, water passing through the inside of the group of heat transfer pipes 25 is cooled and turns into chilled water. This chilled water is utilized as a cooling/heating medium for air conditioning, industrial cooling water, or the like.

The low pressure refrigerant which has been evaporated (gasified) due to heat exchange with the group of heat transfer pipes 25 is subjected to gas-liquid separation by the demister 27. That is, when a gasified low pressure refrigerant (gasified refrigerant) is headed for the refrigerant outlet 23 inside the pressure container 21, a fast flow is formed due to the characteristics of the low pressure refrigerant having specific volume greater than that of a high pressure refrigerant. Then, droplets of the liquid-phase refrigerant which have spouted upward from the low pressure refrigerant pool in a non-gasified state are entrained by the fast flow of the gasified refrigerant and tend to come out through the refrigerant outlet 23, leading to a possibility of occurrence of carry-over.

However, since these droplets are captured by the porous demister 27, are separated, and fall into the low pressure refrigerant pool due to gravity, the droplets are prevented from being carried over. The gasified refrigerant which has been subjected to gas-liquid separation as described above comes out through the refrigerant outlet 23 and is suctioned and compressed again in the turbo compressor 2 via the suction pipe 14. Thereafter, the freezing cycle is repetitively performed.

In the evaporator 7 according to the present embodiment, the separation portion 27A is provided between the circumferential portion of the demister 27 and the inner circumferential surface of the pressure container 21. The separation portion 27A is provided on both the sides 27L and 27R of the demister 27 along the axis direction of the pressure container 21. Since such a separation portion 27A is provided in the demister 27, droplets of a refrigerant which have passed through the demister 27 upward from below can promptly return to a lower part of the demister 27 via the separation portion 27A.

That is, as illustrated in FIG. 5, in a case where the inside of the pressure container 21 having a cylindrical shell shape is seen in the axis direction, a gasified refrigerant which has passed through the demister 27 upward from below forms an upward air current U toward the refrigerant outlet 23 (not illustrated FIG. 5) provided at the center of the upper portion of the pressure container 21. At the same time, a downward air current D drawing a loop downward is formed on both sides of the upward air current U. This downward air current D is headed for the separation portion 27A of the demister 27 along the inner surface of the cylinder-shaped pressure container 21. Therefore, refrigerant droplets R which have passed through the demister 27 can be induced into the separation portion 27A due to the downward air current D and can return to the lower part of the demister 27.

In this manner, the refrigerant droplets R which have passed through the demister 27 upward from below can return to the lower part of the demister 27 via the separation portion 27A formed in the demister 27 by utilizing the downward air current D. Therefore, the quantity of the refrigerant droplets R staying in an upper part of the demister 27 can be reduced and the refrigerant droplets R can be prevented from hitching a flow of a gasified refrigerant and being carried over to the turbo compressor 2 side through the refrigerant outlet 23.

In addition, the separation portion 27A is provided to be biased to the upstream portion side of the group of heat transfer pipes 25. On the upstream portion side of the group of heat transfer pipes 25 inside the pressure container 21 having a cylindrical shell shape, a liquid refrigerant intensely boils due to a significant difference between relative temperatures of the cooling target liquid flowing inside thereof and the liquid refrigerant. However, the boiling degree of the liquid refrigerant decreases toward a downstream side of the group of heat transfer pipes 25.

Therefore, the separation portion 27A is provided to be biased at a position where the liquid refrigerant boils intensely and the refrigerant droplets R are likely to pass through the demister 27, so that the refrigerant droplets R which have passed through the demister 27 can promptly return from the separation portion 27A to the lower part of the demister 27 and can be effectively prevented from being carried over to the turbo compressor 2 side.

Moreover, as a layout of the group of heat transfer pipes 25, the group of outbound pipes 25A in which a difference between relative temperatures of the cooling target liquid flowing inside the heat transfer pipes and the liquid refrigerant is significant as described above and the liquid refrigerant intensely boils is disposed in the lower portion of the pressure container 21. The group of inbound pipes 25B in which the temperature difference between the cooling target liquid and the liquid refrigerant is small and the liquid refrigerant boils gently is disposed in the upper portion of the pressure container 21. Therefore, the liquid refrigerant intensely boils in a deep part of a liquid refrigerant pool inside the pressure container 21, so that the refrigerant droplets R are unlikely to scatter on a liquid surface of the liquid refrigerant.

In addition, due to such a layout in which the group of outbound pipes 25A and the group of inbound pipes 25B vertically overlap each other, for example, compared to a case of a layout in which the group of outbound pipes 25A and the group of inbound pipes 25B laterally overlap each other, the amount of air bubbles of the liquid refrigerant which comes into contact with the group of outbound pipes 25A and boils can be uniform throughout the pressure container 21 in a width direction.

Accordingly, a flow of the upward air current U of the gasified refrigerant in an upper part of the demister 27 is laterally equalized, and a part having a high flow velocity is prevented from being locally generated, so that it is possible to prevent the refrigerant droplets R from being carried over to the turbo compressor 2 side due to a flow of a gasified refrigerant at a high flow velocity.

Moreover, in the present embodiment, the demister 27 is disposed immediately above the group of heat transfer pipes 25. In a case where the low pressure refrigerant is used, since the gas flow velocity is high, the distance to a position where droplets of a liquid refrigerant (refrigerant droplets R) spouting upward are separated from a gasified refrigerant due to their dead weights becomes comparatively long. Therefore, when the demister is installed at a position higher than the position where the droplets are separated due to their dead weights, the distance from the liquid surface of the refrigerant to the demister 27 becomes long, and the pressure container 21 increases in shell diameter.

When the demister 27 is disposed immediately above the group of heat transfer pipes 25 as described above, the quantity of droplets spouting upward is reduced by the demister 27, so that the carry-over amount can be reduced. Moreover, when the demister 27 is disposed immediately above the group of heat transfer pipes 25, evaporated mist of the low pressure refrigerant is promoted to be droplets having a large diameter in the space above the demister 27, and the distance to the position where droplets are separated due to their dead weights is shortened, so that it is possible to prevent the low pressure refrigerant from being carried over.

As described above, according to the evaporator 7 of the present embodiment and the centrifugal chiller 1 provided with the evaporator 7, since the quantity of the refrigerant droplets R above the demister 27 can be reduced, the necessity of reducing the flow velocity of a gasified refrigerant inside the pressure container 21 by increasing the diameter of the pressure container 21 or increasing the pipe pitch of the group of heat transfer pipes 25 decreases.

Therefore, in a case of using a low pressure refrigerant used particularly at the maximum pressure of less than 0.2 MPaG, while compactness of the evaporator 7 is retained, deterioration in efficiency or damage to the device caused by a liquid-phase low pressure refrigerant carried over to the turbo compressor 2 side can be suppressed.

The present invention is not limited to only the configurations of the embodiments described above, and changes or modifications can be suitably added. An embodiment having such changes or modifications added thereto is also included in the scope of rights of the present invention. For example, the shape of the pressure container 21 of the evaporator 7, the layout of each of components inside thereof, and the like are not limited to those of the present embodiment.

REFERENCE SIGNS LIST

-   -   1 CENTRIFUGAL CHILLER     -   2 TURBO COMPRESSOR     -   3 CONDENSER     -   7 EVAPORATOR     -   21 PRESSURE CONTAINER     -   22 REFRIGERANT INLET     -   23 REFRIGERANT OUTLET     -   25 GROUP OF HEAT TRANSFER PIPES     -   25A GROUP OF OUTBOUND PIPES     -   25B GROUP OF INBOUND PIPES     -   26 REFRIGERANT DISTRIBUTION PLATE     -   27 DEMISTER     -   27A SEPARATION PORTION     -   27 a CUT-OUT     -   27L, 27R SIDE OF DEMISTER     -   R REFRIGERANT DROPLET 

1. An evaporator comprising: a pressure container into which a condensed refrigerant is introduced; a refrigerant inlet which is provided in a lower portion of the pressure container; a refrigerant outlet which is provided in an upper portion of the pressure container, a group of heat transfer pipes which passes through an inside of the pressure container and circulates a cooling target liquid inside the group of heat transfer pipes to cause the cooling target liquid to be subjected to heat exchange with the refrigerant; and a demister which is installed between the refrigerant outlet and the group of heat transfer pipes inside the pressure container and performs gas-liquid separation of the refrigerant, wherein a separation portion is provided between a circumferential portion of the demister and an inner circumferential surface of the pressure container.
 2. The evaporator according to claim 1, wherein the pressure container has a cylindrical shell shape extending in a horizontal direction, and wherein the separation portion is provided on a side of the demister along an axis direction of the pressure container.
 3. The evaporator according to claim 1, wherein the pressure container has a cylindrical shell shape extending in a horizontal direction, wherein the group of heat transfer pipes is installed to pass through the inside of the pressure container in a longitudinal axis direction, and wherein the separation portion is provided to be biased to an upstream portion side of the group of heat transfer pipes.
 4. The evaporator according to claim 1, wherein the pressure container has a cylindrical shell shape extending in a horizontal direction, wherein the group of heat transfer pipes includes a group of outbound pipes extending from one end to the other end in the longitudinal axis direction inside the pressure container, and a group of inbound pipes communicating with the group of outbound pipes at the other end in the longitudinal axis direction inside the pressure container and returning from the other end to the one end in the longitudinal axis direction inside the pressure container, and wherein the group of outbound pipes is disposed below and the group of inbound pipes is disposed above inside the pressure container.
 5. The evaporator according to claim 1, wherein the demister is disposed immediately above the group of heat transfer pipes.
 6. A centrifugal chiller comprising: a turbo compressor which compresses a low pressure refrigerant used at a maximum pressure of less than 0.2 MPaG; a condenser which condenses the compressed low pressure refrigerant; and the evaporator according to claim 1, which evaporates the expanded low pressure refrigerant. 